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66-405: The following lists describe programs associated with OS/360 and successors . No DOS , TPF or VM utilities are included. Many of these programs were designed by IBM users, through the group SHARE , and then modified or extended by IBM from versions originally written by a user. These programs are usually invoked via Job Control Language (JCL). They tend to use common JCL DD identifiers (in

132-469: A replacement selection technique to reduce storage usage. The program placed emphasis on sequence distribution techniques , which could be defaulted depending on the number and type of devices available, or could be specified by the user, for making best use of secondary storage "sort work" (SORTWK) files. These techniques were methods of distributing partially sorted sequences of records most efficiently. There were five distribution techniques available to

198-408: A Fixed number of Tasks (MFT) was intended to serve as a stop-gap until Multiprogramming with a Variable number of Tasks (MVT), the intended target configuration of OS/360, became available in 1967. Early versions of MVT had many problems, so the simpler MFT continued to be used for many years. After introducing new System/370 machines with virtual memory in 1972, IBM developed MFT 2 into OS/VS1 ,

264-415: A VSAM key-sequenced data set and copy an ISAM data set into it. IEBPTPCH ("PrinT and PunCH") prints or punches records from a sequential or partitioned dataset. OS/360 and successors OS/360 , officially known as IBM System/360 Operating System , is a discontinued batch processing operating system developed by IBM for their then-new System/360 mainframe computer , announced in 1964; it

330-496: A Variable number of Tasks (MVT) was the most sophisticated of three available configurations of OS/360 's control program, and one of two available configurations in the final releases. MVT was intended for the largest machines in the System/360 family. Introduced in 1964, it did not become available until 1967. Early versions had many problems and the simpler MFT continued to be used for many years. Experience indicated that it

396-474: A decade after their successors had been launched. The division between MFT and MVT arose because of storage limitations and scheduling constraints. Initially IBM maintained that MFT and MVT were simply "two configurations of the OS/360 control program", although later IBM described them as "separate versions of OS/360". IBM originally wrote OS/360 in assembly language . Later on, IBM wrote some OS/360 code in

462-412: A mainstream operating system and is the ancestor of today's widely used VSE . IBM released three variants of OS/360: PCP (Primary Control Program), a stop-gap which could run only one job at a time, in 1966; MFT ( Multiprogramming with Fixed number of Tasks) for the mid-range machines, and MVT (Multiprogramming with Variable number of Tasks) for the top end. MFT and MVT were used until at least 1981,

528-554: A new approach to workload management, allowing users to define performance targets for high-priority batch jobs. This enabled users to give their systems more work than before without affecting the performance of the highest-priority jobs. MVS was IBM's first mainstream operating system on the System/370 to support what IBM called tightly coupled multiprocessing , in which 2 (later, up to 12, for IBM mainframes, and up to 16, for Amdahl mainframes) CPUs shared concurrent access to

594-465: A new implementation of the catalog facility which enables applications to access files by name, without needing to know which disk drive(s) they are on. VSAM datasets must be defined in a VSAM catalog before they are used, and non-VSAM datasets can also be listed in a VSAM catalog. The MVS Master Catalog must be a VSAM catalog. Catalogs were originally provided in OS/360 in the form of CVOLs; MVS added

660-731: A new language, Basic Systems Language (BSL), derived from PL/I. A large amount of the TSO code in Release 20 was written in BSL. TSS/360 was so late and unreliable that IBM canceled it, although IBM later supplied three releases of the TSS/370 PRPQ. By this time CP-67 was running well enough for IBM to offer it without warranty as a timesharing facility for a few large customers. These three options offered such similar facilities that porting applications between them usually required minimal effort;

726-572: A new merge algorithm called BLOCKSET in DFSORT the successor to OS/360 Sort/Merge. Of historical note, the BLOCKSET algorithm was invented by an IBM Systems Engineer in 1963 and was discovered in IBM's archives and implemented in 1990. Sort/Merge is very frequently used; often the most commonly used application program in a mainframe shop generally consuming about twenty percent of the processing power of

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792-533: A number of "user exits" are supported, and these may be load modules (i.e., a member of a library), or object decks (i.e., the output of an assembler), with the Sort/Merge application loading (load modules) or linking (object decks; termed "dynamic link editing" in DFSORT) the exit, as specified and required. Working storage datasets (i.e., SORTWK01, ..., SORTWKnn) may be disk or tape, although the BLOCKSET algorithm

858-666: A separate timesharing operating system, TSS/360 , for the System/360 Model 67 . There are at least two accounts of why IBM eventually decided to produce other, simpler batch-oriented operating systems: IBM introduced a series of stop-gaps to prevent System/360 hardware sales from collapsing—first Basic Programming Support (BPS) and BOS/360 (Basic Operating System, for the smallest machines with 8K byte memories), then TOS/360 (Tape Operating System, for machines with at least 16K byte memories and only tape drives), and finally DOS/360 (Disk Operating System), which became

924-419: A separate article. This article adheres to IBM's usage of the term storage rather than memory . OS/360 assigns processors to tasks, which are analogous to light-weight processes or threads in other systems. Each task has a Task Control Block (TCB) and a stack of Request Blocks (RBs). A task is either dispatchable or nondispatchable and an RB is either waiting or not waiting. The Dispatcher selects

990-445: A separate catalog structure for VSAM; later IBM added a third type of catalog known as an ICF catalog. (IBM removed support for CVOL and VSAM catalogs as of 2000, since they were not Y2K-compliant; hence in z/OS, only ICF catalogs are supported.) In 1974 IBM announced Systems Network Architecture , which was meant to reduce the cost of running large networks of terminals, mainly by using communications lines much more efficiently. This

1056-435: A sequential dataset, or creates a partitioned dataset. Some of the tasks that IEBGENER can perform include the following: An example of an IEBGENER program to copy one dataset to another: For straight copy tasks, the sort program can often do these faster than IEBGENER. Thus many mainframe shops make use of an option that automatically routes such tasks to the sort ICEGENER program instead of IEBGENER. On some systems it

1122-564: A set of libraries on tape that the installation had to restore to DASD in order to perform a system generation . IBM also offered a set of optional source tapes that the installation could use to modify and assemble modules that IBM normally provided as object code. In addition, IBM offered microfiche that had assembly listing of the basic program material and of subsequent service. IBM continued distributing source code until it imposed an Object Code Only (OCO) policy for licensed software. The other major operating system for System/360 hardware

1188-514: A sorted file, or copy selected records. Internally, these utilities use one or more of the standard sorting algorithms , often with proprietary fine-tuned code. Mainframes were originally supplied with limited main memory by today's standards and the amount of data to be sorted was frequently very large. Because of this, unlike more recent sort programs, early Sort/Merge programs placed great emphasis on efficient techniques for sorting data on secondary storage , typically tape or disk . In 1968

1254-466: A while one could find that, although there was enough spare memory in total to run a program, it was divided into separate chunks none of which was large enough. System/360 lacked memory relocation hardware so memory compaction could not be used to reduce fragmentation. A facility called Rollout/Rollin could swap a running job out to secondary storage to make its memory available to another job. The rolled-out job would, however, have to be rolled-in to

1320-512: Is a critical component of many mainframe environments. When migrating from the mainframe to other platforms such as Unix , Linux or Windows , a Sort/Merge utility is needed; MFSORT from Micro Focus and AHLSORT emulate the functions of DFSORT outside of the Mainframe environment. Prior to virtual storage operating systems, "The input data set [was] almost always too large to be brought into main storage and sorted all at once." SORT used

1386-411: Is divided into a system ( fixed ) area at the bottom of real storage, a common area at the top and a private area in the middle. These contain the following areas. 'This is a section of storage at the highest physical address. It contains Mainframe sort merge The Sort/Merge utility is a mainframe program to sort records in a file into a specified order, merge pre-sorted files into

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1452-431: Is only available for IBM's virtual memory operating systems, since its mainframe software component, VTAM is only available with these operating systems. In 1977 IBM announced MVS/System Extensions, a program product (i.e., it cost extra money) which improved MVS performance and added functionality. Descendants of the original MVS are still used on the latest descendants of System/360, System/390 and zSeries ; it

1518-523: Is possible to send email from a batch job by directing the output to the " SMTP " external writer . On such systems, the technique is as follows: It is also possible to attach files while sending the email from Mainframe. IEBIMAGE manipulates several types of definitions (AKA images ) for the IBM 3211 printer, IBM 3800 laser printing subsystem and the IBM 4248 printer. Common uses are for forms control buffers ( FCB s), character arrangement tables, character definitions and images of forms to be printed on

1584-535: Is restricted to disk working storage; more working storage datasets generally improves performance. Sort/merge is important enough that there are multiple companies each selling their own sort/merge package for IBM mainframes and their z/OS , z/VM and z/VSE operating systems . These programs are largely compatible with IBM's SORT programs, often with some extensions. The major Sort/Merge packages are: (Some of these companies also sell versions for other platforms, such as Unix , Linux , or Windows .) Sort/Merge

1650-542: Is specified, the entire namelist must be enclosed in parentheses. When coded with TYPE=POSITION, STEPNAME specifies the first job step to be placed in the output data set. Job steps preceding this step are not copied to the output data set. When coded with TYPE=INCLUDE or TYPE=EXCLUDE, STEPNAME specifies the names of job steps that are to be included in or excluded from the operation. For example, STEPNAME=(STEPA,STEPF-STEPL,STEPZ) indicates that job steps STEPA, STEPF through STEPL, and STEPZ are to be included in or excluded from

1716-519: Is to contain a JOB statement and all job steps belonging to the job except those steps specified in the STEPNAME parameter. STEPNAME=(namelist) specifies the names of the job steps that you want to process. namelist can be a single job step name, a list of step names separated by commas, or a sequential range of steps separated by a hyphen (for example, STEPA-STEPE). Any combination of these may be used in one namelist. If more than one step name

1782-406: Is used to compare two sequential or partitioned datasets . This data set comparison is performed at the logical record level. Therefore, IEBCOMPR is commonly used to verify that a backup copy of a data set is correct (exact match to the original). During processing, IEBCOMPR compares each record from each data set, one by one. If the records are unequal, IEBCOMPR lists the following information in

1848-567: The ISPF SuperC (ISRSUPC) compare program is often used instead. IEBCOPY copies, compresses and merges partitioned data sets . It can also select or exclude specified members during the copy operation, and rename or replace members. Some of the tasks that IEBCOPY can perform include the following: For the IEBCOPY utility , the required job control statements for a copy are as follows: The MYDD1 and MYDD2 DD statements are names chosen by

1914-471: The virtual storage MVS and the 64-bit z/OS , are still run as of 2023 and maintain application-level compatibility with OS/360. IBM announced three different levels of OS/360, generated from the same tapes and sharing most of their code. IBM eventually renamed these options and made some significant design changes: Users often coined nicknames, e.g., "Big OS", "OS/MFT", but none of these names had any official recognition by IBM. IBM provided OS/360 as

1980-870: The OS Dispatcher and the IOS , notably, among many others, remained coded in Assembly Language , which had been enhanced for OS/VS in the IFOX00 Assembler (from the older, OS/360 IEUASM Assembler). The new version's most noticeable feature was that it supported multiple virtual address spaces - different applications thought they were using the same range of virtual addresses, but the new system's virtual memory facilities mapped these to different ranges of real memory addresses. Each application's address space consists of 3 areas: operating system (one instance shared by all jobs); an application area which

2046-604: The OS Nucleus and Scheduler. However, because of quite different behavior and memory requirements, users commonly consider them de facto separate operating systems and refer to them as "early OS/360", "OS/MFT", "OS/MVT", respectively. MFT differs from MVT mainly in the way in which it manages memory: when installing MFT, customers specify in the system generation (SysGen) a fixed number of partitions , areas of memory with fixed boundaries, in which application programs can be run simultaneously. Primary Control Program (PCP)

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2112-611: The OS, now z/OS operating systems) for their data sets: IDCAMS ("Access Method Services") generates and modifies Virtual Storage Access Method (VSAM) and Non-VSAM datasets. IDCAMS was introduced along with VSAM in OS/VS ; the "Access Method" reference derives from the initial "VSAM replaces all other access methods" mindset of OS/VS. IDCAMS probably has the most functionality of all the utility programs, performing many functions, for both VSAM and non-VSAM files. The following example illustrates

2178-484: The OS/360 Sort/Merge program provided five different "sequence distribution techniques" that could be used depending on the number and type of devices available. Historically, the "alias" SORT has been used to refer to an installation's preferred sort program, IBM's Sort/Merge, and third party Sort/Merge programs (i.e., SYNCSORT, CASORT). DFSORT is often referred to by its program name, ICEMAN (component ICE;

2244-499: The SYSOUT: When comparing sequential data sets, IEBCOMPR considers the data sets equal if the following conditions are met: For partitioned data sets , IEBCOMPR considers the data sets equal if the following conditions are met: If ten unequal comparisons are encountered during processing, IECOMPR terminates with the appropriate message. Note: IEBCOMPR is not a very flexible or user-friendly compare program. It can't restrict

2310-489: The Set System Mask (SSM) instruction to serialize disabled code between the two CPUs. For the most part an M65MP system has the same behavior and interfaces as any other MVT system. The keyword parameter SYS=VMS included M65MP as well as uniprocessor MVT. PCP, MFT and MVT provide similar facilities from the point of view of application programs: Some features were available only for MFT and MVT: When System/370

2376-449: The comparison to only certain columns, it can't ignore differences in white space, it doesn't tell you where in the record the difference occurs, and it halts after 10 differences. On the other hand, it is fast, and it is present on all IBM mainframes. So it is very useful when an exact match is expected, such as comparing load modules that have not been reblocked, or checking that a copy worked properly. For comparisons of programs or reports,

2442-690: The fields of the records to be created, including position, length, format, and initialization to be performed. IEBDG can use an existing dataset as input and change fields as specified in the control statements, for example replacing a name field by random alphabetic text. The contents of each field may be varied for each record, for example by rotating the characters in an alphanumeric field left or right for each subsequent record. Example: IEBEDIT selectively copies portions of JCL. An example of an IEBEDIT program: In this example, data set xxxxx.yyyyy.zzzzz should contain job(s) (which should include steps named STEP5, STEP10, and STEP15). This IEBEDIT routine copies

2508-498: The highest priority dispatchable task whose current RB is not waiting. MVS assigns processors to address spaces , which are analogous to processes, and to Service Request Block (SRBs) and tasks within address spaces. Each address space has an Address Space Control Block (ASCB), a queue of SRBs and a queue of TCBs. In OS/360 all storage is visible to all code, although fetch protection may prevent access by unprivileged code to some control blocks or between jobs. Main storage for MVT

2574-470: The last system of this particular line. The first version of MFT shared much of the code and architecture with PCP, and was limited to four partitions . It was very cumbersome to run multiple partitions. Many installations used Houston Automatic Spooling Priority (HASP) to mitigate the complexity. MFT Version II (MFT-II) shared much more of the Control Program and Scheduler code with MVT, and

2640-494: The need for operators to stop the printer and change paper. IEBISAM unloads, loads, copies and prints ISAM datasets. Extracted from IBM manual SC26-7414-08 z/OS DFSMSdfp Utilities: The IEBISAM program is no longer distributed. Starting in z/OS V1R7, ISAM data sets can no longer be processed (created, opened, copied or dumped). ISAM data sets that are still in use must be converted to VSAM key-sequenced data sets. Prior to z/OS V1R7, you could use access method services to allocate

2706-486: The only System/370 operating systems that do not have modern descendants. OS/VS2 release 1 was just MVT plus virtual memory and VSAM (see below). This version was eventually renamed OS/VS2 SVS , for Single Virtual Storage, when OS/VS2 Release 2, also known as MVS, for Multiple Virtual Storage, was introduced. SVS was intended as a stepping stone from MVT to MVS, and is only of historical interest today. In 1974 IBM released what it described as OS/VS2 Release 2 but which

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2772-470: The operation. If STEPNAME is omitted, the entire input job whose name is specified on the EDIT statement is copied. If no job name is specified, the first job encountered is processed. NOPRINT specifies that the message data set is not to include a listing of the output data set. Default: The resultant output is listed in the message data set. See here for more info: [1] IEBGENER copies records from

2838-591: The original OS/360 Sort/Merge program name was IERRCO00, component IER, also with "alias" SORT). Prior to the System/370 , all IBM mainframe operating systems included sort/merge utilities. With the announcement of virtual storage operating systems, DOS/VS and OS/VS , IBM unbundled much of the software and offered chargeable sort/merge program products. For OS/VS IBM offered 5734-SM1, OS Sort/Merge, and later offered 5740-SM1, OS/VS Sort/Merge, subsequently renamed Data Facility Sort (DFSORT). In 1990 IBM introduced

2904-655: The original memory locations when they again became available. In 1971 the Time Sharing Option (TSO) for use with MVT was added as part of release 20.1. TSO became widely used for program development because it provided an editor, the ability to submit batch jobs, be notified of their completion, and view the results without waiting for printed reports, and debuggers for some of the programming languages used on System/360. TSO in OS/360 communicated with terminals by using Telecommunications Access Method (TCAM). TCAM's name suggests that IBM hoped it would become

2970-408: The output along with the text, for company logos to be printed on the page, or just to print 'graybar' pages (alternating gray & white horizontal backgrounds, to match the previous greenbar paper ). With this utility, many different forms or logos could be stored as images, and printed when needed, all using the same standard blank paper, thus eliminating the need to stock many preprinted forms, and

3036-418: The output is to consist of a JOB statement, the job step specified in the STEPNAME parameter, and all steps that follow that job step. All job steps preceding the specified step are omitted from the operation. POSITION is the default. INCLUDE specifies that the output data set is to contain a JOB statement and all job steps specified in the STEPNAME parameter. EXCLUDE specifies that the output data set

3102-440: The output. Default: If START is omitted and only one EDIT statement is provided, the first job encountered in the input data set is processed. If START is omitted from an EDIT statement other than the first statement, processing continues with the next JOB statement found in the input data set. TYPE={POSITION|INCLUDE|EXCLUDE} specifies the contents of the output data set. These values can be coded: POSITION specifies that

3168-404: The same memory (and a single copy of the operating system and peripheral devices), providing greater processing power and a degree of graceful degradation if one CPU failed (which, fortunately, became an increasingly rare event, as system up time rose from hours to days and, then, to years .) Initially MVS was supplied with a job queue manager called JES2 (Job Entry Subsystem 2), which

3234-491: The same versions of most IBM Program Products , application and utility software ran on both. The text below mostly treats PCP , MFT and MVT as simply new names for the original SSS , MSS and MPS , although there were some design changes. Also, the text does not distinguish between M65MP and MVT. Officially, PCP, MFT and MVT are not separate operating systems from OS/360, they are only install-time configuration options—in today's words, three different variants of

3300-504: The selected steps of the job onto the SYSUT2 output file (in this example, the internal reader). The syntax of the EDIT statement is: START=jobname specifies the name of the input job to which the EDIT statement applies. Each EDIT statement must apply to a separate job. If START is specified without TYPE and STEPNAME, the JOB statement and all job steps for the specified job are included in

3366-430: The shop. Modern Sort/Merge programs also can copy files, select or omit certain records, summarize records, remove duplicates, reformat records, append new data and produce reports. Indeed, most Sort/Merge applications use the wide range of additional processing capabilities, rather than purely sorting or merging records: the Sort/Merge product is a very fast way of performing input to and output from these functions. Quite

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3432-534: The standard access method for data communications, but in fact TCAM in OS/VS2 was used almost entirely for TSO and was largely superseded by Virtual Telecommunications Access Method (VTAM) in the mid-to-late 1970s. Also referred to as SYS=VMS in invocations of some macros that were system-dependent. Model 65 Multiprocessing (M65MP) is a variant of MVT. It runs on a 360/65 in Multisystem mode M65MP traps use of

3498-505: The use of IDCAMS to copy a dataset to disk. The dataset has 80-byte records, and the system will choose the block size for the output: In the example above, SYSIN control cards are coming from an in-stream file, but you can instead point to any sequential file or a PDS member containing control cards or a temporary data-set, if you wish. Example of using SYSIN files would be something like this: or this: IEBCOMPR compares records in sequential or partitioned data sets . The IEBCOMPR utility

3564-596: The use of virtual memory. IBM provided an OS/360 SYSGEN option for S/370 support, which did not support DAT but did: OS/VS1 is the successor to MFT, and offers similar facilities with several additions, e.g., RES, virtual memory. VSAM (see below) was initially available as an independent component release (ICR) and later integrated into the OS/VS1 base. IBM released fairly minor enhancements of OS/VS1 until 1983, and in 1984 announced that there would be no more. AIX/370 , AIX/ESA , DPPX , IX/370 , OS/VS1 and TSS/370 are

3630-450: The user for the partitioned input and output data sets, respectively; The defaults are SYSUT1 and SYSUT2. You can use any valid DDNAME for these two DD statements. These DDNAMEs are specified in the utility control statements to tell IEBCOPY the name of the input and output data sets. You only need one DD statement for a PDS to be compressed. IEBDG ('Data Generator') creates test datasets consisting of patterned data. Control statements define

3696-445: The work of all those CPUs. Note: JES1 was the job queue manager for OS/VS1 (see above). IBM hoped that Virtual storage access method (VSAM) would replace its earlier sequential, indexed and direct access methods as it provided improved versions of these: These VSAM formats became the basis of IBM's database management systems , IMS/VS and DB2 - usually ESDS for the actual data storage and KSDS for indexes. VSAM also provides

3762-596: Was DOS/360 . OS/360 is in the public domain and can be downloaded freely. As well as being run on actual System/360 hardware, it can be executed on the free Hercules emulator , which runs under most UNIX and Unix-like systems including Linux , Solaris , and macOS , as well as Windows . There are OS/360 turnkey CDs that provide pregenerated OS/360 21.8 systems ready to run under Hercules. IBM originally intended that System/360 should have only one batch-oriented operating system, OS/360, capable of running on machines as small as 32 KiB. It also intended to supply

3828-472: Was announced in 1970 it offered essentially the same facilities as System/360 but with about 4 times the processor speeds of similarly priced System/360 CPUs. Then in 1972 IBM announced System/370 Advanced Functions , of which the main item was that future sales of System/370 would include virtual memory capability and this could also be retro-fitted to existing System/370 CPUs. Hence IBM also committed to delivering enhanced operating systems which could support

3894-509: Was descended from HASP ( Houston Automatic Spooling Priority ) and also supported Remote Job Entry from workstations located elsewhere. JES2 can only manage jobs for one CPU (which might be a tightly coupled multiprocessor system). In 1976 IBM provided another option, JES3 (Job Entry Subsystem 3), a descendant of ASP ( Attached Support Processor ), which allows one CPU to manage a single job queue feeding work to several physically distinct CPUs, and therefore allows one operator's console to manage

3960-544: Was influenced by the earlier IBSYS/IBJOB and Input/Output Control System (IOCS) packages for the IBM 7090/7094 and even more so by the PR155 Operating System for the IBM 1410 / 7010 processors. It was one of the earliest operating systems to require the computer hardware to include at least one direct access storage device . Although OS/360 itself was discontinued, successor operating systems, including

4026-583: Was intended for machines with small memories. It is similar to MFT with one partition . Experience indicated that it was not advisable to install OS/360 on systems with less than 128 KiB of memory, although limited production use was possible on much smaller machines, such as 48 KiB of memory. IBM dropped the PCP option in the final releases of OS/360, leaving only MFT II and MVT, both of which required more memory. Also referred to as SYS=MIN in macro expansions that were system-dependent. Multiprogramming with

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4092-509: Was much more flexible to run. The maximum number of partitions increased to 52. Later modifications of MFT-II added sub-tasking , so that the fixed number of tasks was no longer fixed, although the number of partitions did remain a limitation. Experience indicated that it was not advisable to install MFT on systems with less than 256 KiB of memory, which in the 1960s was quite a large amount. Also referred to as SYS=INT in macro expansions that were system-dependent. Multiprogramming with

4158-426: Was not advisable to install MVT on systems with less than 512 KiB of memory. MVT treated all memory not used by the operating system as a single pool from which contiguous regions could be allocated as required, by an unlimited number of simultaneous application and systems programs. This scheme was more flexible than MFT's and in principle used memory more efficiently, but was liable to fragmentation - after

4224-400: Was really a new operating system that was upwards-compatible with OS/VS2 Release 1. The Supervisor of the new system had been largely rewritten in a new dialect of BSL, PL/S ; BSL and PL/S were dialects of PL/I with extensions designed to transcribe Assembly language code, including privileged instructions needed to control the computer as a whole. Time-sensitive OS components, such as

4290-478: Was renamed to OS/390 for System/390, and the 64-bit version for the zSeries was named z/OS . For reasons of size, this section concentrates on the MVT option of OS/360; PCP and MFT are very similar; with changes in nomenclature and some minor differences. OS/VS1 and SVS have much the same structure as MFT II and MVT, while MVS , although retaining much of the logic of MVT, has major enhancements better addressed in

4356-567: Was unique for each application; shared virtual area used for various purposes including inter-job communication. IBM promised that the application areas would always be at least 8MB. This approach eliminated the risk of memory fragmentation that was present in MVT and SVS, and improved the system's internal security. The new system rapidly became known as " MVS " (Multiple Virtual Storages), the original OS/VS2 became known as "SVS" (Single Virtual Storage) and IBM itself accepted this terminology and labelled MVS's successors "MVS/ xxx ". MVS introduced

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